The invention relates to a laser system and, more particularly, to an upcollimator structure of a laser system that enables control of fluence and power density at an image area of the laser system.
Conventionally, the modulation of fluence and power density (peak power density) of a laser system is achieved by varying the power output of the laser, attenuating the power, varying the repetition rate of the laser, or changing the position of the workpiece in relation to the focal plane of the respective laser system. These methods have distinct disadvantages in controlling the fluence and or power density at the workpiece. For example, changing the repetition rate of the laser will cause instability and lead to a certain predetermined set of conditions. The entire range of desired fluence and power density settings cannot be scanned. In addition, the repetition rate cannot be used to create changes in less than one second intervals for a given laser source due to the resonator instability and first pulse phenomena. Thus, changing the repetition rate of the laser tends to introduce a large amount of variability in the fluence and power density.
In addition, using the pumping power to change the laser power output has similar disadvantages as described above with regard to the changing the repetition rate.
The power attenuation is an excellent machine design to adjust the fluence and the power density in terms of the stability, but it relies on a measurement and feedback loop to determine the power at or somewhere in the optical train of the laser system. There is also a loss in the throughput of the system, since some of the beam is used for feedback purposes. Another important item is that the attenuation will need to be set to 5-10% lower than the maximum fluence and/or power density to have an effective control system.
None of the aforementioned machine features can effectively control the depth of focus.
Accordingly, there is a need to provide an upcollimator structure for a laser system that can easily control fluence and power density at an image area of the system.
An object of the invention is to fulfill the need referred to above. In accordance with the principles of the present invention, this objective is achieved by providing an upcollimator structure for a laser system. The upcollimator structure includes at least one concave lens; at least one convex lens spaced from the concave lens; and at least one lens member composed at least in part of piezoelectric material disposed between the lenses or a lens member mounted on a positioner. When voltage is applied to the lens member, a refractive index of the lens member changes thus changing an upcollimation factor when a light beam is passed through the upcollimator structure.
In accordance with another aspect of the invention, an upcollimator structure for a laser system includes a first lens structure including at least one concave lens, and a second lens structure including at least one convex lens. At least one of the lenses is composed at least in part of piezoelectric material, whereby, when voltage is applied thereto, a refractive index thereof changes thus changing an upcollimation factor when a light beam is passed through the upcollimator structure.
In accordance with yet another aspect of the invention, a method of controlling fluence and power density of a laser system which generates a light beam is provided. The laser system has an upcollimator structure including as an optical system, at least one convex lens, at least one concave lens spaced from the convex lens, and at least one lens member, composed at least in part of piezoelectric material, disposed between the convex lens and the concave lens. The method includes directing the light beam through the optical system at a first fluence setting and a first power density setting, and supplying voltage to the lens member to change a refractive index of the lens member and directing the light beam through the optical system thereby providing a second fluence setting and a second power density setting.
The lens member can be moved with respect to the convex lens and the concave lens thereby changing the upcollimation and focal point of the light beam as the light beam exits the optical system to provide a third fluence setting and a third power density setting.
Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification.